1. Field of the Invention
The present invention relates to a display having a touch sensor and a method for improving the touch performance thereof.
2. Discussion of the Related Art
Along with the trend of light weight and slim size of home electronic appliances and portable information devices, user input means is switching from a button switch to a touch screen. The touch screen refers to a screen through which a user can enter data by directly touching the screen. Starting with use in the mobile phone market, the use of touch screens is expanding across comprehensive ranges of IT products.
A touch screen applied to a display comprises a plurality of touch sensors. The touch sensors may be incorporated as in-cell type in a display panel, or coupled, as on-cell type or add-on cell type, to the display panel. Touch types are classified into a resistive type, a capacitive type, an electro-magnetic type, etc. Among them, the capacitive type for detecting a touched portion by detecting a position where a capacitance change has occurred is widely used.
Capacitive type touch sensors comprise sensor nodes, respectively, which are formed at intersections of a plurality of Tx lines and a plurality of Rx lines to constitute a mutual capacitor. The capacitive type touch sensors recognize a touch position by calculating a change in the capacitance of the mutual capacitor between before and after a touch.
Since a capacitive type touch screen comprises a few touch sensors for each pixel of the display panel, its physical resolution is lower than the physical resolution of the display panel. Therefore, an operation of correcting a difference in physical resolution between the touch screen and the display panel is performed in a display having a touch sensor, before executing an application program associated with coordinate values of a touch position. By a resolution correction operation, touch coordinates detected with a resolution level of the touch screen are converted into those with a resolution level of the display panel, as shown in FIG. 1.
A known resolution correction technique includes a method of multiplying a resolution increase ratio by touch coordinates detected with a resolution level of a touch screen. For example, if the resolution of the display panel is A*B and the touch coordinates detected with the resolution level of the touch screen (C*D)(C<A,D<B) are X,Y, and the existing resolution correction technique is used, X is converted into a coordinate value incremented by A/C, and Y is converted into a coordinate value incremented by B/D.
In such a conventional resolution correction technique, calculation is performed only on the coordinates of a touch sensor with the largest change in capacitance, without considering surrounding touch sensors. This makes accurate coordinate matching difficult at the time of resolution conversion, thus making it difficult for a user t display a desired execution result on the display panel. In an example, even if the user draws a straight or curve on the touch screen, it will be distorted, as is the aliasing phenomenon shown in FIG. 2, when actually displayed on the display panel. The conventional resolution correction technique alone will not suffice to improve touch performance.